1. Field of the Invention
The invention is generally related to the field of heterocyclic chemistry and the synthesis of nitrogen heterocycles, and more specifically to an improved process for the synthesis of 4-amino-1,2,4-triazole.
2. General Background
The compound 4-amino-4H-1,2,4-triazole (ATA) is important because it can be used to make 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) by the Vicarious Nucleophilic Substitution (VNS) process as set forth in U.S. Pat. No. 5,569,783 to Mitchell, et al. In the VNS reaction, picramide is treated with either hydroxylamine or ATA, which causes the two remaining aromatic hydrogen atoms to be replaced by amine (—NH2) groups. Although ATA produces TATB of better quality than hydroxylamine, ATA is very expensive to purchase ($250/kg). Organic Synthesis, Collective Vol. III describes how to synthesize ATA.
The VNS method is better than the traditional process for TATB because the traditional process used trichlorobenzene, a chlorocarbon compound, as the feedstock. In contrast, the VNS method starts with chlorine-free picramide. Thus, the resulting TATB produced by the VNS method is free of chloride.
U.S. Pat. No. 5,099,028 discloses a method to make ATA. However, the method starts with a carboxylic acid. In the disclosed method 91% formic acid is mixed with 100% hydrazine hydrate and a catalyst, Amberlyst 15 ion exchange resin. Water is distilled off between 105 and 150 degrees Celsius, and the reaction mixture is held at 150 degrees Celsius for six hours. The mixture is then cooled to 80 degrees Celsius, isopropanol is added, the resin is filtered off and rinsed with isopropanol, and the combined filtrates are cooled to precipitate ATA. The slurry is filtered to isolate ATA. Reportedly, the yield is 80%, the purity is 99.5%, and the melting point is between 87 and 89 degrees Celsius. The patent also refers to the use of ethyl formate as a reactant as being undesirable. However, the present invention uses ethyl formate as a reactant with a catalyst such as Amberlyst 15 to produce a satisfactory product at a time and temperature that are within a usable range.
Some of the prior methods require 24 hours for the synthesis of ATA.